1. Field of the Invention
The invention relates to an image display system for displaying a dot clock signal on the basis of a horizontal sync signal and for displaying an image.
2. Related Background Art
FIG. 5 shows a conventional example of an image display system.
A host computer 1 is connected to a display unit 2 through a signal line 3. The host computer 1 transmits sync signals (horizontal sync signal, vertical sync signal) and an image signal to the display unit 2 through the signal line 3. A dot clock corresponding to the image signal is not transmitted from the host computer 1 through the signal line 3, the dot clock is reproduced in the display unit 2 on the basis of the horizontal sync signal. Generally, such a reproduction is performed by a PLL (Phase Locked Loop) circuit (not shown) in the display unit 2.
Now assuming that the host computer 1 corresponding to the display of (800.times.800) dots is switched to another host computer corresponding to the display of (1024.times.1024) dots, a frequency of the horizontal sync signal which is transmitted through the signal line 3 changes and, at the same time, the display dots and synchronizing frequency of the image signal which are transferred from such another host computer do not coincide with those of the display unit 2, so that the image display is not optimized.
Therefore, in order to inform the display unit 2 of the fact that the host computer (display information) was changed, the user sets a diagnosis software to such another host computer and sends a specific pattern to the display unit 2 through the signal line 3 for a predetermined time. The display unit 2 detects the specific pattern and stores the frequencies of the sync signals, dot clock, image display period, and the like and initializes a register and the like in the display unit 2 in order to match those parameters with those of such another host computer.
Such operations are also executed in case of exchanging a graphic card in the host computer.
As mentioned above, each time the host computer or graphic card is exchanged, the diagnosis has to be executed, so that it is very troublesome.